The role of leaf and soil analyses in vineyard management (Part 1)

Is it worth the effort for producers to take regular soil and leaf samples, or does this only generate more data without adding real value?

Soil and leaf samples both play a distinct role in the vineyard monitoring process. The way in which they also complement each other gives producers a better understanding of the complex plant-soil interactions. Soil analyses reflect the chemical balances that are present in the root zone and indicate the concentrations, inter alia, of elements that are available for uptake by the plant roots, in other words plant accessible nutrients. Leaf analyses on the other hand are an indication of the ability of the plant roots to take up and utilise the available nutrients given a specific set of circumstances. A leaf sample is a direct measurement of the grapevine’s nutrient status at the specific moment when the sample is taken. A combination of these analyses is especially important to accurately identify problems, monitor and determine a nutritional programme for a vineyard.

This series of three articles will present a comprehensive look at sampling, timing of sampling and the procedure during sampling with a view to soil and leaf analyses. The series will also discuss three types of fertilisation/chemical recommendations:

● Before a new vineyard is established and before the soil analysis is done, namely stock fertilisation.
● During the lifespan of a productive vineyard, evaluation and adjustment of fertilisation programmes every third year, namely maintenance fertilisation.
● Problem cases where deficiencies are observed or when weak spots occur in a vineyard block.

Johan de Jager engaged in soil analysis with a view to vineyard establishment.

The objectives of soil analyses are:

● To characterise the chemical properties of the soil in order to recommend cultivation practices and applications of fertiliser, lime and gypsum that will create an optimal root zone for the plant, as well as ensure optimal nutrient uptake.
● To serve as a basis for balanced fertilisation programmes and to monitor fertilisation practices.
● To quantify problem situations in order to enable adjustments.
● To evaluate biological activity in the soil in order to monitor nematode populations and soil-borne diseases inter alia. These samples should be handled according to specific prescriptions. To obtain the best results, sampling should be done at specific times only.
● Note that the concentrations of the plant nutrients as reported in an analysis represent plant accessible values, in other words the nutrients that are available for uptake by the grapevine.

Soil samples taken at various depths.

Deficiency symptoms in grapevine leaves.

Johan evaluates the preparation action.

The objectives of leaf analyses are:

● To aid evaluation of the plant’s nutrient uptake ability.
● To evaluate the effect of the fertilisation programme on the nutrient status of the grapevine.
● To evaluate the relationship between the soil nutrient status and the plant’s reaction as an aid to fertilisation management/adjustments.
● To diagnose probable nutrient deficiencies during the growing season.
● It is probably not necessary to sample all the blocks annually. Identify a number of monitoring blocks that are representative of the farm and sample these regularly. This enables one to build up a history/norm for the farm. New analyses should then be interpreted in the light of “farm norms”. This will also help producers to understand seasonal variations in analyses.

All the above-mentioned aspects impact on the profitability of the farming enterprise, either with regard to production volumes, fruit quality, lifespan of a block or production cost. Furthermore these contribute to the ecological sustainability of the farming system, especially by preventing mismanagement of fertilisation (excessive application).

Soil and leaf analyses are a useful tool in the hand of the fertilisation consultant. Based on scientific and economic principles, said analyses should combine the vineyard’s nutrient requirements and production goals in a practical and manageable programme. It is very important to know the physical nature of the soil in addition to its chemical composition in order to give optimal advice about fertilisation. Therefore it is of cardinal importance to make profile pits.

Fertilisation is not spot input, in other words the environment, climate and management system should be taken into account when the programme is drawn up. The programme should also include management of the cover crops. Cover crops play an important role in the accumulation of organic matter in the soil, the improvement of soil health and the conservation of biodiversity.

Several local analytical laboratories comply with high standards and provide good service. Also note that the norms being used to interpret the analyses are based on specific analytical methods used by the local laboratories. Producers have no need to submit samples to overseas laboratories.

Meticulous sampling is required, both with regard to the correct procedure and place. Any analysis and recommendation cannot be better than the sample received by the laboratory. Fertilisation programmes, lime applications, leaf nutrition, problem solving and nematode treatments are based on the analyses of the samples that were submitted. In order to obtain the best technical recommendation and economic value, the best possible sample should be analysed.

Example of a satellite image.

Example of an NDVI image.

Many technological aids are available to assist producers with better management decisions. Producers may use data sources, such as satellite images, NDVI, EMI scans, FruitLook, etcetera. One should nevertheless remember that even though measurements fall within the ambit of these technologies, as does the indication of variations and problem areas, they are mostly unable to identify problems. Although the data are sometimes presented in an impressive format, interpretation is key as is processing of the information before it becomes useful to the producer. Identification of the problems or ground truthing still requires experts to visit the areas, make profile pits, take samples, make vineyard observations, interpret analyses, etcetera.

The customary practice is to take one composite soil sample per block/management unit. Sometimes large variations occur within blocks as a result of differences in nutrient status, salt accumulation, drainage, texture, and so forth. In such instances composite samples may dilute the variation analysis and fail to indicate true problem spots. An approach to address this potential problem is to take more intensive samples in a grid pattern (grid sampling or point samples). A less intensive and usually more practical approach is to identify a zone (smart sampling) in a block and combine the samples in order to analyse one representative sample. This zone may be identified by studying soil borders or yield charts.

It is important to take soil and leaf samples from areas with similar characteristics. If necessary, divide the block into smaller zones with similar vigour, yields, soil texture, slope and drainage. It is important, however, that these units should constitute manageable zones, especially in terms of irrigation and fertilisation. Fine-tuning management of smaller existing production systems is extremely difficult. Within such zones/blocks sampling can be either in a random or zig-zag pattern, as long as care is taken that samples are uniform and distributed across the entire area.

In instances where there are problematic areas, such as lower yield or inadequate grapevine growth, these should be sampled separately to determine the reasons for the poor plant performance in the respective areas. This will enable the producer to solve the problems by means of the necessary managerial inputs.

The correct procedures for soil and leaf sampling are discussed in a subsequent article.